Speakers that can be placed close to the back wall

The most important factor in choosing a speaker that's going to live close to walls is how the bass is tuned. Walls/boundaries will boost bass, possibly by a large amount. If you have a typical QB3/flat bass tuning and put that speaker close to a wall, you'll end up with 6db or more bump in the bottom couple octaves ... end result is a thick, muddy sound.

The ideal tuning for near wall placement is an Extended Bass Shelf. Even sealed boxes aren't always ideal for near wall, and can suffer the same effect as I said above, because there's no way to replicate an EBS curve with a sealed enclosure.

Unfortuantely most manufacturers don't tell you what type of tuning they employ. Instead you have to rely on anecdotal evidence like "I have brand x close to a wall and it sounds great", or the manufacturer marketing speak without any explination of why.

ATC sealed -- they love high power, too!

Vapor1 A question: Do any of your speakers use the EXtended Bass Shelf? I thought that technique only used front ported designs? Could you explain more in detail? Thanks!

Hey Chuck, yes we use the EBS alignment on some of our designs and it definately helps make boomy bass a non-issue. Front ported or rear ported, makes no difference ... it's the length of the port and size of the cabinet that determines tuning.

One of the major reasons why most manufacturers don't use EBS tunings is because they typically require about twice the cabinet volume. However, that's one of the benefits to using AudioTechnology woofers, Per Skaaning will build them custom to our specs - so we're able to get a woofer that can tune to an EBS alignment in a .75cu/ft cabinet. Normally that's impossible with a 7" woofer.

To show you a bit more about what an EBS alignment actually is, look at this image that I found quickly using google

http://www.hometheatershack.com/forums/attachments/ported-subwoofer-build-projects/32772d1316499344-sonosub-design-titanic.jpg

That's not a 'real' EBS, but close enough for illustration. The green line would be your standard QB3 alignment, grey would be an EBS-3, and red and EBS-6. The -3 and -6 mean just that, down 3db and 6db from flat. We use EBS-3 alignments because -6 is too much 'shelving down' in our opinion.

You can see how in a real room where bass is boosted, if the tuning is flat, you will end up with a bump. However if you start with the grey line, that bump will be much more benign and overall in-room response will be closer to flat. You can also see how EBS alignments actually give more bottom end extension.

The downside to an EBS alignment is you give up a bit of power handling.

Vapor1. Interesting that you're focusing below 100 Hz instead of more typical diffraction loss or BSC below 500 Hz with, say, a 9 inch wide baffle. Something to do with the speaker depth?